I don't take ocp for contraception but when i had unprotected sex, i took estradiol+levonorgestrel after 4 days. can this be harmful?

Not really: You've described a birth control pill. If you just took one pill, that won't work well as a morning-after pill. So if you were trying to conceive, it probably won't interfere. Birth control pills have not been linked with significant risk of birth defects. Good luck!

Risks ; Benefit: I assume your took the pill as the "plan b" or the "morning-after pill"--but just so you know, this should be taken with in 72 hours, the earlier the better, for it to be effective. After 72 hours, benefit is unclear/less. Risk is breakthrough bleeding, cramps, blood clot (higher if smoker, older age, other med use). Consult doc. Good luck.